ISSN 0036-0244, Russian Journal of Physical Chemistry, 2006, Vol. 80, No. 6, pp. 1004–1005. © Pleiades Publishing, Inc., 2006.
Original Russian Text © A.A. Maerle, I.F. Moskovskaya, V.V. Yushchenko, B.V. Romanovskii, 2006, published in Zhurnal Fizicheskoi Khimii, 2006, Vol. 80, No. 6, pp. 1145–1146.
SHORT
COMMUNICATIONS
Interaction of Metallic Iron Particles with Molecular Hydrogen
A. A. Maerle, I. F. Moskovskaya, V. V. Yushchenko, and B. V. Romanovskii
Faculty of Chemistry, Moscow State University, Leninskie gory, Moscow, 119992 Russia
Received September 15, 2005
DOI: 10.1134/S0036024406060306
In the context of the problem of hydrogen-based metallic Fe at 465–597°ë [7]. According to the data [8–
energetics, which is currently gaining in importance, 10], such a significant temperature shift in the reduction
metal–hydrogen systems, specifically Fe–ç2 systems,
came to the attention of researchers. It is known [1] that
bulk metallic iron absorbs molecular ç2 to yield inter-
stitial solid solutions with a hydrogen content no higher
than 0.1 wt %. On the other hand, bulk hydrides Feçı
(ı ≤ 1) arise in iron–hydrogen systems only at suffi-
ciently high pressures [2–4], at which they are thermo-
dynamically instable. Meanwhile, using the molecular
beam technique [5, 6], it was shown that, at 110 K in a
deep vacuum, small clusters of metallic iron (to several
tens of Fe atoms) retain ~2 H atoms per Fe atom in the
cluster. We have found an analogous effect in the reduc-
tion of iron oxide nanostructures: the absorption of
hydrogen in excess of the stoichiometric amount.
Iron oxide nanostructures were obtained by the
method of isolation in a matrix: in-situ thermal oxida-
tive decomposition of a Fe-containing precursor
adsorbed in a porous inorganic matrix. For the precur-
sor, trinuclear iron dodecacarbonyl Fe3(CO)12 was
used. Porous crystalline materials (molecular sieves
with spatially ordered systems of channels and cavi-
ties)—microporous NaY zeolite (pore size 0.8 nm) and
mesoporous MCM-41 silicate (3.0 nm)—and amor-
phous Silochrom S-120 silica gel (30 nm) were used as
matrices.
Iron carbonyl Fe3(CO)12 used as the precursor was
dissolved in toluene and introduced into the matrices so
that the total Fe content of samples was no higher than
1 wt %. After the removal of the solvent, the samples
were oxidized at 550°ë in a flow of air for 6 h. Iron
oxide formed in pores of the support was reduced in a
flow of Ar containing 3.5 vol % H2. A bulk Fe2O3 sam-
ple was investigated for reference. The reduction was
carried out in the regime of linear rise of temperature
(8 K/min) to 1000°C with the measurement of the rate
of absorption of hydrogen. The total absorbed amount
of hydrogen was determined by the area under the
obtained temperature-programmed reduction (TPR)
curve.
of iron oxides points to the formation of oxide nano-
structures, which are located in pores of the matrix and
not on its outer surface.
Total absorbed amounts of ç2 for the reduction of
iron oxide in the investigated samples and bulk Fe2O3
are listed below:
*
MCM-41 SiO2 Fe2O3
Matrix
NaY
Fe, wt % 0.12 0.41 0.69 0.15 0.13 0.31 70
H2/Fe
3.5
4
2.5
2
1.7
0.5
4.3
5
3.6
4
2.8
2
1.5
H/Fe**
–
*Bulk oxide.
**Less the amount consumed for the reduction.
From the data obtained, it follows that the total
absorbed amount of ç2 in the TPR of bulk Fe2O3 corre-
sponds to the stoichiometric ratio (1.50) for the com-
plete reduction of the sample to metallic iron. In check
experiments on TPR with initial matrices, ç2 was not
absorbed over the entire investigated temperature range
(20–1000°ë); therefore, the difference between the
total absorbed amount of ç2 measured for an Fe-con-
taining sample and the amount required for its complete
reduction corresponds to the amount of hydrogen held
in metallic iron nanoclusters. Quantitative estimates of
this amount are listed above as H/Fe atomic ratios.
For Fe10 metallic iron clusters in conditions of high
vacuum, H/Fe = 1.8 [6], which is in sufficiently close
agreement with our data obtained in the regime of tem-
perature-programmed reduction of iron oxide at a par-
tial ç2 pressure of ~3.5 kPa. From the obtained data, it
follows that, at the lowest metallic iron concentration in
the zeolite matrix, the nanophase holds to 6–8 wt % of
hydrogen.
Thus, metallic iron nanoclusters absorb molecular
hydrogen not only in a vacuum but also in ordinary con-
ditions; in this case, hydride-like compounds formed
TPR curves of the investigated samples have two
temperature regions of reduction of iron oxide with
maximums at 480 and 800°ë. In the bulk sample, are significantly enriched in hydrogen as compared to
Fe2O3 is reduced to Fe3O4 at 380–397°C, and Fe3O4, to the bulk phase.
1004
Maerle
